The rear bag on the port side of the boat fills by itself. It fills when the boat is underway or if any of the other bags are filling. I have checked the soleniod valve and it is in the correct position, any other ideas? Also my ballast pump system filter leaks ( a steady drip) is this normal or should I put some teflon tape or something similar on the threads?

Your value is not operating properly, check the switch located on the value for that sac. Otherwise your value need to be cleaned since it must be open. I had the same problem and the switch on the value was in the open position.

Brad- do mean "valve", because I am not sure what "value" is unless you mean the position of the switch on the valve...?

Bill- yeah that is the same valve, but what Jim G and I are saying is that we have already checked the switch and it is in the correct position, but the bag still fills... I am going to take it apart and see what happens, but I have feeling I am going to have to replace that valve